The present invention relates to emulsion polymers and to coating compositions prepared therefrom.
In recent years there has been a trend toward the preparation of coating compositions from polymeric latexes for environmental reasons. Namely, coating compositions prepared from polymeric latexes do not have the solvent emissions problems associated with normal solvent based coating compositions. Polymeric latexes, however, generally require the presence of a low molecular weight emulsifier or surfactant in order to stabilize the latex particles. Unfortunately, the low molecular weight emulsifiers have been found to adversely affect several properties of coating compositions prepared from such latexes. Specifically, the low molecular weight emulsifiers adversely affect the water sensitivity and adhesion of the coatings and in addition lead to poor weather resistance and degradation by ultraviolet rays and foaming during preparation of the latex and application of the coating.
Another problem associated with emulsion polymers and which is exacerbated by the use of insufficient amounts of low molecular weight emulsifiers or surfactants is the formation of grit in the latex. Grit consists of large chunks of polymeric material which flocculate and settle out. One way in which to minimize or remove the presence of grit is by the addition of additional emulsifier or surfactant. However, as has been mentioned above, the low molecular weight emulsifier leads to other problems which detract from film properties. The grit is also deleterious to the appearance of the coating film because it leads to an undesirable textured appearance and also additional processing costs since in order to remove the grit, the latex must be filtered. Moreover, once the grit is filtered there is the additional cost of disposal since it is a polymeric waste product.
There is a need, therefore, for an emulsion polymer composition which is comparable to conventional materials heretofore available, and in addition which provides coatings having excellent water resistance and corrosion resistance, good adhesion to the substrate and especially outdoor weather resistance and durability.